Wave Optics - 2 PPT Physics Class 12

 Page 1


WAVE  OPTICS - II
1. Electromagnetic Wave
2. Diffraction
3. Diffraction at a Single Slit
4. Theory of Diffraction
5. Width of Central Maximum and Fresnel’s Distance
6. Difference between Interference and Diffraction
7. Polarisation of Mechanical Waves
8. Polarisation of Light
9. Malus’ Law
10.Polarisation by Reflection – Brewster’s Law
11.Polaroids and their uses
Page 2


WAVE  OPTICS - II
1. Electromagnetic Wave
2. Diffraction
3. Diffraction at a Single Slit
4. Theory of Diffraction
5. Width of Central Maximum and Fresnel’s Distance
6. Difference between Interference and Diffraction
7. Polarisation of Mechanical Waves
8. Polarisation of Light
9. Malus’ Law
10.Polarisation by Reflection – Brewster’s Law
11.Polaroids and their uses
0
Electromagnetic Wave:
X
E
0
B
0
Y
Z
Wave is propagating along X – axis with speed c = 1 / vµ
0
e
0
For discussion of EM wave, more significance is given to Electric Field, E.
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The speed of electromagnetic wave depends entirely on the electric and 
magnetic properties of the medium, in which the wave travels and not on 
the amplitudes of their variations.
Page 3


WAVE  OPTICS - II
1. Electromagnetic Wave
2. Diffraction
3. Diffraction at a Single Slit
4. Theory of Diffraction
5. Width of Central Maximum and Fresnel’s Distance
6. Difference between Interference and Diffraction
7. Polarisation of Mechanical Waves
8. Polarisation of Light
9. Malus’ Law
10.Polarisation by Reflection – Brewster’s Law
11.Polaroids and their uses
0
Electromagnetic Wave:
X
E
0
B
0
Y
Z
Wave is propagating along X – axis with speed c = 1 / vµ
0
e
0
For discussion of EM wave, more significance is given to Electric Field, E.
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The speed of electromagnetic wave depends entirely on the electric and 
magnetic properties of the medium, in which the wave travels and not on 
the amplitudes of their variations.
Diffraction of light:
The phenomenon of bending of light around the corners and the 
encroachment of light within the geometrical shadow of the opaque obstacles 
is called diffraction.
S
•
S
•
Diffraction at a slit Diffraction at an obstacle
X
Y
X
Y
X & Y – Region of diffraction
Slit
Obstacle
Screen
Screen
Page 4


WAVE  OPTICS - II
1. Electromagnetic Wave
2. Diffraction
3. Diffraction at a Single Slit
4. Theory of Diffraction
5. Width of Central Maximum and Fresnel’s Distance
6. Difference between Interference and Diffraction
7. Polarisation of Mechanical Waves
8. Polarisation of Light
9. Malus’ Law
10.Polarisation by Reflection – Brewster’s Law
11.Polaroids and their uses
0
Electromagnetic Wave:
X
E
0
B
0
Y
Z
Wave is propagating along X – axis with speed c = 1 / vµ
0
e
0
For discussion of EM wave, more significance is given to Electric Field, E.
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The speed of electromagnetic wave depends entirely on the electric and 
magnetic properties of the medium, in which the wave travels and not on 
the amplitudes of their variations.
Diffraction of light:
The phenomenon of bending of light around the corners and the 
encroachment of light within the geometrical shadow of the opaque obstacles 
is called diffraction.
S
•
S
•
Diffraction at a slit Diffraction at an obstacle
X
Y
X
Y
X & Y – Region of diffraction
Slit
Obstacle
Screen
Screen
Diffraction of light at a single slit:
1) At an angle of diffraction ? = 0°: 
O
0  
1   
2  
3  
4  
5  
6  
7  
8  
9 
10 
11 
12
•
•
•
•
•
•
•
•
•
•
•
•
•
A
B
•
? = 0°
Slit
Screen
Plane 
Wavefront
The wavelets from the single wavefront reach the centre O on 
the screen in same phase and hence interfere constructively
to give Central or Primary Maximum (Bright fringe).
Bright
D
d
Page 5


WAVE  OPTICS - II
1. Electromagnetic Wave
2. Diffraction
3. Diffraction at a Single Slit
4. Theory of Diffraction
5. Width of Central Maximum and Fresnel’s Distance
6. Difference between Interference and Diffraction
7. Polarisation of Mechanical Waves
8. Polarisation of Light
9. Malus’ Law
10.Polarisation by Reflection – Brewster’s Law
11.Polaroids and their uses
0
Electromagnetic Wave:
X
E
0
B
0
Y
Z
Wave is propagating along X – axis with speed c = 1 / vµ
0
e
0
For discussion of EM wave, more significance is given to Electric Field, E.
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The speed of electromagnetic wave depends entirely on the electric and 
magnetic properties of the medium, in which the wave travels and not on 
the amplitudes of their variations.
Diffraction of light:
The phenomenon of bending of light around the corners and the 
encroachment of light within the geometrical shadow of the opaque obstacles 
is called diffraction.
S
•
S
•
Diffraction at a slit Diffraction at an obstacle
X
Y
X
Y
X & Y – Region of diffraction
Slit
Obstacle
Screen
Screen
Diffraction of light at a single slit:
1) At an angle of diffraction ? = 0°: 
O
0  
1   
2  
3  
4  
5  
6  
7  
8  
9 
10 
11 
12
•
•
•
•
•
•
•
•
•
•
•
•
•
A
B
•
? = 0°
Slit
Screen
Plane 
Wavefront
The wavelets from the single wavefront reach the centre O on 
the screen in same phase and hence interfere constructively
to give Central or Primary Maximum (Bright fringe).
Bright
D
d
B
A
Slit
Screen
2) At an angle of diffraction ? = ?
1
:
The wavelets from the single wavefront diffract at an angle ?
1
such 
that BN is ? and reach the point P
1
. The pairs (0,6), (1,7), (2,8), (3,9), 
(4,10), (5,11) and (6,12)  interfere destructively with path difference 
?/2 and give First Secondary Minimum (Dark fringe).
O
0  
1   
2  
3  
4  
5  
6  
7  
8  
9 
10 
11 
12
P
1
N
?
?
1
?
1
?
1
?/2
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Plane 
Wavefront
Bright
Dark
The slit is imagined to be divided into 2 equal halves.